The present invention relates, in general, to transistor amplifiers, and more specifically, to a transistor amplifier utilizing feedback control and impedance matching to provide improved linear and return loss performance characteristics.
Without limiting the scope of the invention, its background is described in connection with a transistor amplifier.
Transistor amplifiers, for example, transistor amplifiers used in the receiver or transmitter chain of mobile communications equipment, may require specific amount of linear power with minimum distortion and a select amount of gain. The amount of linear power and gain may be provided by properly biasing the transistor amplifier. Proper biasing provides the linear power and gain required for a specific application. However, biasing the transistor amplifier also produces input and output impedance. The input and output impedance must also be a conjugate match with the impedance of terminating circuitry to minimize return loss and therefore maintain the amount of gain selected.
A transistor amplifier designed for a specific amount of linear power and a select amount of gain may result in an impedance mismatch with terminating circuitry causing a return loss and therefore a decrease in gain. Therefore, often a transistor amplifier is designed with a compromise in either the amount of linear power provided or the amount of gain delivered. If a specific amount of linear power is required, depending on terminating circuitry a certain amount of gain degradation due to return loss may be accepted. If a select amount of gain is required, the transistor amplifier may be biased for a compromised amount of linear power so that minimal return loss may be realized.
Prior techniques may have included compromising between the amount of linear power provided or the amount of gain delivered or additional circuitry may have been added to isolate the transistor amplifier from terminating circuitry so that a select amount of linear power and gain could be realized. A prior art transistor amplifier may have been biased for a select amount of linear power without consideration of terminating circuitry by utilizing an isolator to isolate the transistor amplifier from the terminating circuitry. An isolator used to provide isolation between the transistor amplifier and the terminating circuitry provides the impedance match required to minimize return loss without affecting the amount of gain and linear power provided. However, isolating circuitry significantly increases size and cost.
As may be seen, a transistor amplifier providing improved linear and return loss performance characteristics could prove to be a useful article of manufacture.
The present invention provides an improved transistor amplifier providing improved linear and return loss performance characteristics.
A transistor amplifier utilizes a dual loop feedback control circuit and an impedance matching circuit to provide improved linear and return loss performance characteristics. The transistor amplifier for coupling between a sending circuit providing a RF signal containing modulated information at a predetermined frequency and a receiving circuit having a load resistance receiving an RF output signal having improved linear and return loss performance characteristics. The transistor amplifier utilizes dual loop feedback control to provide output impedance required for a select amount of linear power. The transistor amplifier further utilizes impedance matching circuitry to allow a conjugate match between the output impedance and the load resistance allowing for the delivery of a select amount of linear power with minimal return loss.
In an embodiment, the transistor amplifier comprises a transistor for linearly amplifying the input signal, the transistor having a base, a collector and an emitter, the base having an input impedance, the collector having an output impedance. The dual loop feedback control circuit comprises a series feedback resistor electrically coupled between the emitter and a ground potential and a shunt feedback resistor electrically coupled between the collector and base. The dual loop feedback control circuit converts the input impedance to a conjugate of the source resistance and the output impedance to optimum load impedance. The impedance matching circuit electrically coupled between the collector and the receiving circuit converts the load resistance to a conjugate of the output impedance and the output impedance to a conjugate of the load resistance at the predetermined frequency.